JPWO2018074511A1 - Fiber laser device - Google Patents

Abstract

The seed light unit (MO) as a fiber laser device amplifies light for amplification, which is a plurality of optical paths shared by a part and resonates light, and a part of each optical path resonates in each optical path. The fiber (13) is disposed in a shared portion of each optical path, and is oscillated at a predetermined cycle to emit light incident from the optical path to the optical path, and light incident from the optical path to other than the optical path AOM (14) switched to the second state, and a resonance period of the light having the largest power among respective lights resonating in the respective optical paths, and a predetermined period in which the AOM (14) vibrates in the first state And are mutually non-integral multiple relationships.

Description

  The present invention relates to a fiber laser device that emits pulsed output light.

  A fiber laser device that amplifies and emits signal light with a rare earth-doped fiber is used as one of laser processing devices used for processing using laser light and medical equipment such as a scalpel using laser light. ing. As one of such fiber laser devices, an MO-PA (Master Oscillator Power Amplifier) type fiber laser device that amplifies and emits seed light is known. The seed light unit, which is an MO unit that emits seed light of the fiber laser device, may be configured of a fiber laser device that emits light excited based on the excitation light as seed light.

  In Patent Document 1 below, a resonance type fiber laser device for exciting light between a pair of FBGs (Fiber Bragg Gratings) sandwiching both ends of an amplification optical fiber, and a part as an amplification optical fiber are looped. A fiber ring type fiber laser device is described which excites light in the optical path. In these fiber laser devices, a Q switch is used to emit pulsed light. In general, the Q switch is composed of an acousto-optic element (AOM: Acoustic Optic Modulation), and the acousto-optic element propagates incident light in different directions in the on state and the off state. When the acoustooptic device is on, the acoustooptic device propagates light so that part of the light emitted from the amplification optical fiber is incident on the amplification optical fiber. Therefore, light emitted from the amplification optical fiber and incident again on the amplification optical fiber is amplified, and the amplified light is emitted. On the other hand, when the acousto-optic element is off, the light is propagated so that the light emitted from the amplification optical fiber does not enter the amplification optical fiber again.

JP, 2012-164860, A

  By the way, in the acousto-optic element, a state in which it vibrates in synchronization with an input RF signal is generally turned on. The present inventors have found that in the light emitted from the fiber laser device described in Patent Document 1 described above, ripples synchronized with the oscillating period of the acousto-optic element may occur, and this ripple may be increased. Found.

  Then, an object of this invention is to provide the fiber laser apparatus which can suppress the ripple of the light to radiate | emit.

  The present inventors diligently studied the cause of the increase in ripple synchronized with the period in which the acousto-optic element vibrates. As a result, it has been found that the ripple may be increased due to the relationship between the period in which the acoustooptic element vibrates and the optical path length at which the light to be amplified resonates. Therefore, the inventors of the present invention have made further studies to reach the present invention.

  That is, according to the present invention, there are provided a plurality of optical paths in which a part is shared and light is resonated, an amplification optical fiber which is a part of each optical path and amplifies each light resonating in each optical path; The first state is disposed in the shared portion of the optical path, and vibrates at a predetermined cycle to emit light incident from the optical path to the optical path, and the second state emits light incident from the optical path to other than the optical path And an acousto-optic element switched to the resonant cycle of the light having the largest power among respective lights resonating in the respective optical paths, and the predetermined cycle in which the acousto-optic element vibrates in the first state. Are in a relationship of non-integer multiples with each other.

  The inventors of the present invention have found that the ripple increases when the period of oscillation of the acousto-optic element in which the ripple is synchronized coincides with the period at which light resonates in the optical path. Furthermore, it has been discovered that the ripple becomes large not only when the respective periods coincide but also when the period of oscillation of the acousto-optic element and the period at which light resonates the optical path have an integral multiple relationship with each other. did. Further, in the fiber laser device having a plurality of optical paths, it is considered that the ripple of the light with the largest power among the lights resonating in the respective optical paths has the largest influence on the ripple of the emitted light. In the present invention, the resonance period of the light having the largest power and the predetermined period in which the acousto-optic element vibrates are in the relation of a non-integer multiple. That is, the resonance period of the light with the largest power is a non-integer multiple of the predetermined period of the vibration of the acoustooptic element, and the predetermined period of the vibration of the acoustooptical element is the noninteger multiple of the resonance period of the light with the largest power. It is assumed. By setting the resonance period of the light with the largest power and the predetermined period in which the acousto-optic element vibrates to be a noninteger multiple relationship with each other as described above, it is possible to suppress that the most noticeable ripple is large. For this reason, according to the fiber laser device of the present invention, it is possible to suppress the ripple of the emitted light.

  Further, it is preferable that the respective resonance periods of the respective lights resonating in the respective optical paths and the predetermined period in which the acousto-optic element vibrates in the first state be in a relation of a non-integer multiple.

  By setting the resonance period of each light and the predetermined period in which the acousto-optic element vibrates to be a non-integer multiple relationship with each other, it is possible to suppress an increase in the ripple of each light.

  Further, the plurality of optical paths have a specific optical path, and an optical path including the specific optical path and a circular loop optical path connected in the middle of the specific optical path, and the light propagating through the specific optical path Preferably branches into the loop optical path with a predetermined branching ratio, and light propagating through the loop optical path is coupled to the specific optical path with the predetermined branching ratio.

  When the optical path length of a specific optical path becomes long, the waveform of light resonating with the optical path tends to have a wave of a cycle longer than the ripple. However, by providing the loop light path as described above, the undulation can be suppressed.

  In this case, the specific optical path may be an optical path in which light reciprocates between the pair of reflecting portions. When light reciprocates and resonates, part of the light can propagate in the loop light path between the forward path and the return path. Therefore, the variation of the optical path is increased, and the above-mentioned undulation can be further suppressed.

  As described above, when the specific optical path is an optical path in which light reciprocates between a pair of reflecting portions, the predetermined branching ratio is 3 dB or less, and the resonance period of light resonating in the specific optical path; The predetermined period in which the acousto-optical element vibrates in the first state may be set to a noninteger multiple relationship.

  In light emitted from a fiber laser device in which light resonates in an optical path in which light travels back and forth between a pair of reflecting portions, when the branching ratio is 3 dB or less, light propagating in a specific optical path without propagating in a loop optical path. The inventors found that the power is the highest. For this reason, with the above-described configuration, the resonance period of the light with the largest power and the predetermined period in which the acoustooptic device vibrates are in a relation of a non-integer multiple, and the most noticeable ripple can be suppressed.

  In addition, as described above, when the specific light path is a light path in which light reciprocates between a pair of reflecting portions, the predetermined branching ratio is set to 3 dB or more and 4.8 dB or less, and it is in the middle of propagating the specific light path. The resonant cycle of the light resonating in the optical path that travels around the loop optical path and the predetermined cycle in which the acousto-optic element vibrates in the first state are mutually set to a noninteger multiple relationship Also good.

  In the light emitted from the fiber laser device in which light resonates in a light path in which light travels back and forth between a pair of reflecting portions, a loop light path is generated in the middle of a specific light path when the branching ratio is 3 dB or more and 4.8 dB or less unlike the above The present inventors have found that the power of light propagating around one round is the highest. For this reason, with the above-described configuration, the resonance period of the light with the largest power and the predetermined period in which the acoustooptic device vibrates are in a relation of a non-integer multiple, and the most noticeable ripple can be suppressed.

  In addition, as described above, when the specific light path is a light path in which light reciprocates between a pair of reflecting portions, the predetermined branching ratio is set to 4.8 dB or more, and the light beam travels along the specific light path. The resonance period of the light resonating in the optical path that makes two rounds of the loop optical path and the predetermined period in which the acousto-optic element vibrates in the first state may be in a relation of a noninteger multiple .

  In light emitted from a fiber laser device in which light resonates in an optical path in which light travels back and forth between a pair of reflecting parts, when the branching ratio is 4.8 dB or more, the loop optical path is made twice around the specific optical path. The present inventors have found that the power of light propagating is the highest. For this reason, with the above-described configuration, the resonance period of the light with the largest power and the predetermined period in which the acoustooptic device vibrates are in a relation of a non-integer multiple, and the most noticeable ripple can be suppressed.

  Further, as described above, in the case where the specific light path is a light path in which light reciprocates between a pair of reflecting portions, it is preferable that the predetermined branching ratio be 2 dB or more and 8 dB or less.

  In the case where the predetermined branching ratio is 2 dB or more and 8 dB or less, light propagating in a specific optical path without propagating in the loop optical path, light propagating in one loop optical path in the middle of a specific optical path, and intermediate in the specific optical path The power of each light resonating in a plurality of optical paths, such as light propagating in two rounds of the loop optical path and light propagating in three rounds of the loop optical path in the middle of a specific optical path, is balanced. The inventors have found. Therefore, by setting the branching ratio as described above, even when undulation occurs in each light, it is possible to suppress the undulation of specific light from being noticeable, and it is possible to reduce the undulation of emitted light.

  In addition, the specific light path may be a circular light path. With such a configuration, it is possible to suppress the ripple in the fiber ring type fiber laser device.

  As described above, according to the present invention, a fiber laser device capable of suppressing ripples of emitted light is provided.

It is a figure showing a fiber laser device of MO-PA type which has a fiber laser device concerning a 1st embodiment of the present invention as a light source. It is a figure which shows typically the mode of the magnitude | size of the power of the light radiate | emitted from each site | part of FIG. It is a figure which shows typically the mode of the pulse-form light radiate | emitted from a seed light part. It is a figure which shows the relationship between the ratio of the power of each light which resonates in each light path of a seed light part, and is radiate | emitted from a seed light part, and the branch ratio in an optical coupler. It is a figure which shows the fiber laser apparatus of MO-PA type which has a fiber laser apparatus concerning 2nd Embodiment of this invention as a light source. It is a figure which shows the time change of the intensity | strength of the light radiate | emitted from the optical system of a comparative example and an Example. It is an enlarged view of the part enclosed with the dotted line of FIG.

  Hereinafter, preferred embodiments of a fiber laser device according to the present invention will be described in detail with reference to the drawings.

First Embodiment
FIG. 1 is a view showing a fiber laser device according to the present embodiment.

  As shown in FIG. 1, the fiber laser device 1 includes a seed light unit MO that emits seed light, a preamplifier PR that amplifies the seed light emitted from the seed light unit MO, a main amplifier PA, and a seed light unit MO. A wavelength conversion unit RF provided between the preamplifier PR and a wavelength selection filter FL provided between the wavelength conversion unit RF and the main amplifier PA are mainly included. As described above, the fiber laser device 1 is a so-called MO-PA type fiber laser device in which the seed light unit MO is a master oscillator and the main amplifier PA is a power amplifier.

<Configuration of seed light portion MO>
The seed light portion MO includes: an excitation light source 11 for emitting excitation light; an amplification optical fiber 13 to which excitation light emitted from the excitation light source 11 is incident and an active element to be excited by the excitation light is added; An FBG (Fiber Bragg Grating) 12 as a first reflecting portion provided on one end side of the optical fiber 13, and an acoustooptical element (AOM) 14 connected to the other end of the amplification optical fiber 13 and also serving as a second reflecting portion; An optical coupler 16 provided between the FBG 12 and the AOM 14 and a loop optical fiber 15 connected to the optical coupler 16 are provided as main components. As described above, the seed light unit MO is formed of a resonant type fiber laser device.

  The excitation light source 11 of the seed light portion MO is a light source for emitting continuous light, and is constituted of, for example, a laser diode. The excitation light source 11 emits excitation light of a wavelength that excites the active element to be added to the amplification optical fiber 13, for example, light having a wavelength of 915 nm. Further, the excitation light source 11 is connected to the first optical fiber 18, and the light emitted from the excitation light source 11 of the seed light portion MO propagates in the first optical fiber 18.

  The amplification optical fiber 13 of the seed light portion MO has a core and a cladding that surrounds the outer peripheral surface of the core without a gap. In the amplification optical fiber 13, the refractive index of the core is higher than the refractive index of the cladding, and as a material constituting the core, for example, an element such as germanium which raises the refractive index, and the excitation light source 11 of the seed light portion MO And quartz doped with an active element such as ytterbium (Yb), which is excited by the light of the seed light portion emitted therefrom. Examples of such active elements include rare earth elements. Examples of rare earth elements include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), erbium (Er), etc. in addition to Yb. It can be mentioned. In addition to the rare earth elements, examples of the active element include bismuth (Bi). Moreover, as a material which comprises the clad of the optical fiber 13 for amplification, the pure quartz which the dopant is not added at all is mentioned, for example.

  The first optical fiber 18 is connected to one end of the amplification optical fiber 13, and the core of the first optical fiber 18 and the core of the amplification optical fiber 13 are optically coupled. Further, an FBG 12 is provided in the core of the first optical fiber 18. Thus, the FBG 12 is provided on one end side of the amplification optical fiber 13. In the FBG 12, a portion where the refractive index is increased with a constant period is repeated along the longitudinal direction of the first optical fiber 18, and by adjusting this period, the amplification optical fiber 13 in the excited state is obtained. Among the light emitted by the active element, light of a specific wavelength is configured to be reflected. In the case where the active element added to the amplification optical fiber 13 is ytterbium as described above, for example, the reflectance of light having a wavelength of 1060 nm is 100%.

  One end of a second optical fiber 19 is connected to the other end of the amplification optical fiber 13. The configuration of the second optical fiber is the same as that of the first optical fiber, and the core of the second optical fiber 19 and the core of the amplification optical fiber 13 are optically coupled.

  The loop optical fiber 15 has the same configuration as the first optical fiber 18 and the second optical fiber 19, and is connected to the second optical fiber 19 in the optical coupler 16 provided in the middle of the second optical fiber 19. Specifically, in a state where one end and the other end of the optical fiber constituting the loop optical fiber 15 are connected, the portion including the one end and the other end and the second optical fiber 19 are twisted each other a predetermined number of times and melted. It is worn. A portion where the second optical fiber 19 and the loop optical fiber 15 are fused in this manner becomes an optical coupler 16. For this reason, in the optical coupler 16, the core of the second optical fiber 19 and the core of the loop optical fiber 15 are optically coupled at a predetermined branching ratio.

  The branching ratio means the following two ratios. One of the ratios is branched from the second optical fiber 19 to the loop optical fiber 15 with respect to the power of light propagating through the second optical fiber without branching from the second optical fiber 19 to the loop optical fiber 15 in the optical coupler 16 It is the ratio of the power of light. The other ratio is coupled in the optical coupler 16 from the loop optical fiber 15 to the second optical fiber 19 with respect to the power of light propagating in the loop optical fiber 15 without being coupled from the loop optical fiber 15 to the second optical fiber 19. It is the ratio of the power of light. In this case, the respective ratios are equal to one another. When the power ratio is expressed in decibels, for example, if it is 3 dB, light of about 50% power of the light propagating through the second optical fiber 19 and entering the optical coupler 16 is the second optical fiber 19 The remaining light of about 50% power branches into the loop optical fiber 15. Therefore, when the branching ratio approaches 0 dB, the light propagating through the second optical fiber 19 hardly branches into the loop optical fiber 15. This branching ratio is the above-described predetermined value in which the optical fiber constituting the loop optical fiber 15 and the second optical fiber 19 are mutually twisted when the loop optical fiber 15 and the second optical fiber 19 are fused as described above. It is determined by the number of times.

  The other end of the second optical fiber 19 is connected to the AOM 14. The AOM 14 can switch between the first state and the second state. The first state is a state in which the AOM 14 is turned on, and the AOM 14 vibrates at a predetermined cycle. In the first state, light incident from the core of the second optical fiber 19 propagates the AOM 14 toward the preamplifier PR and causes Fresnel reflection on the end face of the AOM 14 on the preamplifier PR side, and the light again enters the core of the second optical fiber 19. It emits toward the head. The reflectance of the Fresnel reflection is lower than the reflectance of the FBG 12. In the second state, the AOM 14 vibrates in a cycle different from the state in which the AOM 14 is turned off or in the first state. In the second state, light incident from the core of the second optical fiber 19 propagates in the AOM 14 in a direction different from that in the first state. Therefore, in the second state, the light incident on the AOM 14 is emitted in a direction different from that of the second optical fiber 19.

  As described above, in the seed light portion MO of the present embodiment, light reciprocates along the optical path formed by a part of the first optical fiber 18, the amplification optical fiber 13, the second optical fiber 19, and the AOM 14 and resonates. Do. Assuming that this optical path is a specific optical path, and the circular optical path formed of the loop optical fiber 15 is a loop optical path, the seed light portion MO includes not only the specific optical path but also an optical path consisting of the specific optical path and the loop optical path. It will have. An optical path consisting of a specific optical path and a loop optical path is an optical path different from the specific optical path, and shares a part with the specific optical path. The light propagating through this optical path is branched from the second optical fiber 19 to the loop optical fiber 15 in the optical coupler 16 and goes around the loop optical fiber 15 one or more turns, and then the optical coupler 16 It is coupled to the optical fiber 19. Further, even in the case of an optical path including a loop optical path, the optical paths are different from each other if the number of times of looping around the loop optical fiber 15 is different. Thus, since the loop optical fiber 15 is connected to a specific optical path, the optical path lengths of the respective optical paths are different from each other, and the resonance periods of the respective lights resonating in the respective optical paths are different from each other.

In the present embodiment, at least the resonance period of the light having the largest power among the lights resonating in the respective optical paths described above and the predetermined period in which the AOM 14 vibrates in the first state have a non-integer multiple relationship. It is assumed. In other words, the resonance cycle of the light with the largest power among the respective lights resonating in the respective optical paths is a non-integer multiple of the predetermined cycle in which the AOM 14 vibrates in the first state, and the AOM 14 vibrates in the first state. The period is a non-integer multiple of the resonance period of the light with the largest power among the respective light resonating in the respective optical paths. Furthermore, it is preferable that the respective resonance periods of the respective lights resonating in the respective optical paths described above and the predetermined period in which the AOM 14 vibrates in the first state be in a relation of a non-integer multiple. In this case, the respective resonance cycles of the respective lights resonating in the respective optical paths are set to be non-integer multiples of the predetermined cycle in which the AOM 14 vibrates in the first state, and the predetermined cycles in which the AOM 14 vibrates in the first state are the respective. It is a non-integer multiple of each resonance period of each light resonating in the light path. For example, when the frequency at which the AOM 14 vibrates is 135 MHz, the vibration period is 74 × 10 ⁻¹⁰ seconds. Assuming that the specific optical path length is a basic optical path length S, the speed of light is 299, 792, 458 m / s, and the refractive index of the optical fiber is 1.445, the speed of light in the substance is 1 / refractive index Therefore, if the basic optical path length S is 1 m, the resonance period of light resonating a specific optical path is equal to about 1.0 × 10 ^-8 seconds equivalent to the time for reciprocating the specific optical path. In this case, the resonance period of light resonating in a specific optical path and the predetermined period in which the AOM 14 vibrates in the first state are in a relation of a non-integer multiple. In addition, when the basic optical path length S is 1 m and the loop optical path length L which is the length of the loop optical fiber 15 is 0.5 m, the resonance of the resonating light in the optical path which makes one round of the loop optical path while the light resonates. The period is about 1.3 × 10 ^-8 seconds, and in the case of an optical path in which the loop optical path is made twice while the light resonates, the resonant period of the resonating light is about 1.5 × 10 ^-8 seconds. Therefore, in this case, the respective resonance periods of the respective lights resonating in the respective optical paths and the predetermined period in which the AOM 14 vibrates in the first state are in the relation of a non-integer multiple.

  The amplification optical fiber 13 is a part of each optical path, and the AOM 14 is disposed in the shared part of each optical path.

<Configuration of Preamplifier PR>
The preamplifier PR mainly includes a pump light source 21, an amplification optical fiber 23, and a coupler 22.

  The excitation light source 21 of the preamplifier PR is constituted of, for example, a plurality of laser diodes, and excitation light of a wavelength for exciting the active element to be added to the amplification optical fiber 23 of the preamplifier PR as described later Emit The excitation light source 21 is connected to the optical fiber 28, and the excitation light emitted from the excitation light source 21 propagates through the optical fiber 28. Examples of the optical fiber 28 include a multimode fiber, and in this case, the excitation light propagates through the optical fiber 28 as multimode light.

  The amplification optical fiber 23 of the preamplifier PR has a core, an inner cladding surrounding the outer peripheral surface of the core without a gap, and an outer cladding covering the outer peripheral surface of the inner cladding. In the amplification optical fiber 23, the refractive index of the core is higher than the refractive index of the inner cladding, and the refractive index of the inner cladding is higher than the refractive index of the outer cladding. That is, the amplification optical fiber 23 has a double clad structure. In the amplification optical fiber 23, as a material constituting the core, for example, the same material as the core of the amplification optical fiber 13 of the above-mentioned seed light portion MO can be mentioned, and as a material constituting the inner cladding, For example, the same material as that of the cladding of the amplification optical fiber 13 of the seed light portion MO can be mentioned. Moreover, as a material which comprises the outer clad of the optical fiber 23 for amplification, an ultraviolet-ray cured resin can be mentioned, for example.

  In the present embodiment, the AOM 14 of the seed light portion MO is connected to the optical fiber 29. The coupler 22 connects the optical fiber 29 and the optical fiber 28 to one end of the amplification optical fiber 23. Specifically, in the coupler 22, the core of the optical fiber 29 is connected to the core of the amplification optical fiber 23, and the core of the optical fiber 28 is connected to the inner cladding of the amplification optical fiber 23. . Accordingly, light emitted from the AOM 14 of the seed light portion MO is incident on the core of the amplification optical fiber 23 via the optical fiber 29 and propagates through the core. The excitation light emitted from the excitation light source 21 is incident on the inner cladding of the amplification optical fiber 23 and mainly propagates in the inner cladding. Therefore, the light propagating in the core is amplified by the stimulated emission of the active element excited by the excitation light emitted from the pumping light source 21 by the light propagating in the core of the amplification optical fiber 23.

<Configuration of Wavelength Converter RF, Wavelength Selection Filter FL>
The wavelength conversion unit RF is connected to the amplification optical fiber 23 of the preamplifier PR. Among the incident light, the wavelength conversion unit RF converts light having a power greater than a predetermined power into light having a longer wavelength than the incident light and emits the light, and in the incident light, a light having a power smaller than a predetermined power , Leave the wavelength of the incident light.

  As such a wavelength conversion unit RF, there can be mentioned a Raman optical fiber which causes stimulated Raman scattering. Examples of this Raman optical fiber include an optical fiber in which a core is doped with a dopant that raises the nonlinear optical constant. Such dopants include germanium and phosphorus. When the wavelength conversion unit RF is a Raman optical fiber, the threshold of the intensity of the light to be converted can be changed depending on the diameter of the core, the doping concentration of the dopant, the length, and the like.

  The light emitted from the preamplifier PR enters the wavelength selection filter FL via the wavelength conversion unit RF. Then, when light whose wavelength is converted in the wavelength conversion unit RF is incident, the light is transmitted toward the main amplifier PA, and when light whose wavelength is not converted in the wavelength conversion unit RF is incident, the main amplifier PA of this light Transmission to the Therefore, when the light emitted from the preamplifier PR is wavelength-converted by the wavelength conversion unit RF, the light incident on the wavelength selection filter FL is transmitted from the wavelength selection filter FL toward the main amplifier PA. On the other hand, when the light emitted from the preamplifier PR is not wavelength converted in the wavelength conversion unit RF, the transmission of the light incident on the wavelength selection filter FL from the wavelength selection filter FL to the main amplifier PA is suppressed. As such a wavelength selection filter FL, for example, a WDM coupler or a dielectric multilayer film filter can be mentioned.

<Configuration of Main Amplifier PA>
Unlike the preamplifier PR in that the main amplifier PA amplifies incident light at a higher amplification factor than the preamplifier PR, the main amplifier PA mainly includes a plurality of excitation light sources 31, an amplification optical fiber 33, and a coupler 32.

  Each of the excitation light sources 31 of the main amplifier PA is constituted of, for example, a plurality of laser diodes, and excitation light of a wavelength for exciting the active element to be added to the amplification optical fiber 33 of the main amplifier PA as described later It emits excitation light of 915 nm. Each excitation light source 31 is connected to an optical fiber 38, and the excitation light emitted from each excitation light source 31 propagates in each optical fiber 38. Each optical fiber 38 is, for example, similar to the optical fiber 28 connected to the excitation light source 21 of the preamplifier PR. In this case, the excitation light propagates through the optical fiber 38 as multimode light.

  The amplification optical fiber 33 of the main amplifier PA has the same configuration as the amplification optical fiber 23 of the preamplifier PR.

  Further, in the present embodiment, the wavelength selection filter FL is connected to the optical fiber 39. The coupler 32 connects the optical fibers 39 and the respective optical fibers 38 to one end of the amplification optical fiber 33. Specifically, in the coupler 32, the core of the optical fiber 39 is connected to the core of the amplification optical fiber 33, and the cores of the respective optical fibers 38 are connected to the inner cladding of the amplification optical fiber 33. ing. Accordingly, the light emitted from the wavelength selection filter FL toward the main amplifier PA is incident on the core of the amplification optical fiber 33 via the optical fiber 39 and propagates through the core, and the excitation light emitted from the respective excitation light sources 31 The light enters the inner cladding of the amplification optical fiber 33 and propagates mainly in the inner cladding. Therefore, the light propagating through the core is amplified by the stimulated emission of the active element excited by the excitation light emitted from the pumping light source 31 by the light propagating through the core of the amplification optical fiber 33.

  An optical fiber 40 is connected to the other end of the amplification optical fiber 33 of the main amplifier PA. The optical fiber 40 is an optical fiber that propagates the light emitted from the amplification optical fiber 33 to a predetermined place and emits the light, and may be called a delivery optical fiber.

<Operation of Fiber Laser Device 1>
Next, an operation of emitting pulsed light from such a fiber laser device 1 will be described.

  In the fiber laser device 1 of the present embodiment, the excitation light is always emitted from the excitation light source 11 of the seed light portion MO, and in the standby state, the AOM 14 of the seed light portion MO is brought into the second state. Accordingly, the light entering the AOM 14 from the second optical fiber 19 is emitted to the outside without being reflected to the second optical fiber 19. Therefore, light does not resonate in the optical path between the FBG 12 and the end face of the AOM 14 on the preamplifier side, that is, the specific optical path or the optical path consisting of the specific optical path and the loop optical path. For this reason, the excited state of the active element of the amplification optical fiber 13 becomes high. Further, in the present embodiment, in the standby state, the respective excitation light sources 21 and 31 are in the emission state. Therefore, active elements to be added to each of the amplification optical fiber 23 of the preamplifier PR and the amplification optical fiber 33 of the main amplifier PA are brought into the excited state. The period in which the AOM 14 of the seed light portion MO is in the second state is a period in which the amplification optical fiber 13 does not oscillate. Further, the period in which the excitation light is incident on the amplification optical fiber 23 and the amplification optical fiber 33 is a period in which self-oscillation does not occur. Therefore, in the standby state, the emission of unintended giant pulse light from the amplification optical fibers 13, 23, 33 is suppressed.

  Next, the AOM 14 is brought into the first state at a timing slightly before the point of time when the pulsed light is emitted. Then, an optical path between the FBG 12 and the end face on the preamplifier side of the AOM 14, that is, a specific optical path including a part of the first optical fiber 18, the amplification optical fiber 13, the second optical fiber 19 and the AOM 14 The light reciprocates along the optical path including the specific optical path and the loop optical path, and the light resonates in each of the optical paths. By this resonance light, the active element of the amplification optical fiber 13 in the high excitation state as described above causes stimulated emission, the resonance light is amplified, and the pulse light is emitted from the AOM 14, and the seed light portion MO Pulsed light as light is emitted.

  FIG. 2 is a diagram showing the state of the magnitude of the power of light emitted from each part at the time of emission of pulsed light. Specifically, the power of the light emitted from the seed light portion MO, the light emitted from the preamplifier PR, the light emitted from the wavelength conversion portion RF, the light emitted from the wavelength selection filter FL, and the power of the light emitted from the main amplifier PA It is a figure which shows the appearance of the time change of wavelength, and a wavelength. In the portions of FIG. 2 showing temporal changes in light power, the vertical axis shows the power density of light, and the horizontal axis shows time.

  The shape of the temporal change of the power of the pulsed light emitted from the seed light portion MO is a Gaussian distribution. Further, the wavelength of the pulsed light emitted from the seed light portion MO is, for example, 1060 nm. As described above, pulsed light emitted from the seed light portion MO is incident on the core of the amplification optical fiber 23.

  As described above, in the amplification optical fiber 23 of the preamplifier PR, the active element is brought into the excited state by the excitation light. Therefore, when pulsed light is incident on the amplification optical fiber 23 from the seed light portion MO, the excited active element causes stimulated emission by the light from the seed light portion MO, and the power of the light is amplified by the stimulated emission. As a result, pulsed light is emitted from the amplification optical fiber 23. The amplification optical fiber 23 emits the light of the Gaussian distribution shape in which the power density is amplified with respect to the incident light when the light with the temporal change of the power enters the Gaussian distribution shape. Therefore, as shown in FIG. 2, from the preamplifier PR, light having a Gaussian distribution shape in which the shape of the temporal change of the power is extended in the direction of the power density with respect to the light emitted from the seed light portion MO is emitted.

  A part of the light emitted from the preamplifier PR is a power density to be wavelength converted by the wavelength conversion unit RF. Therefore, in the wavelength conversion unit RF, among the light incident from the preamplifier PR, the light component having a power density higher than a specific power density is regarded as primary scattered light. For example, when the wavelength of light emitted from the seed light unit MO is 1060 nm as described above, the wavelength of light having a power larger than a predetermined power is set to, for example, 1120 nm in the wavelength conversion unit RF. Then, from the wavelength conversion unit RF, light which is not wavelength converted and primary scattered light are emitted. The shape of the temporal change of the power of light emitted from the wavelength conversion unit RF is the same as the shape of the temporal change of the power of light emitted from the preamplifier PR. Among these, as shown in FIG. 2, the light of wavelength 1060 nm which is not wavelength converted is the light of low power density including the footing portion in the Gaussian distribution shape, and the light of the wavelength 1120 nm which is primary scattered light is the vertex of the Gaussian distribution shape It is light with high power density including a part.

  The light emitted from the wavelength conversion unit RF enters the wavelength selection filter FL. As described above, the wavelength selective filter FL transmits this light toward the main amplifier PA when the light subjected to wavelength conversion in the wavelength conversion unit RF is incident, and the light which is not wavelength converted in the wavelength conversion unit RF Suppress transmission towards the main amplifier PA. Therefore, transmission of the light having a small power density which is not subjected to wavelength conversion among the light emitted from the preamplifier PR as shown by the broken line in FIG. 2 is suppressed, and emitted from the preamplifier PR shown by the solid line in FIG. The primary scattering of light passes through the wavelength selection filter FL. The pulse width of this primary scattered light is made smaller than the pulse width of the light emitted from the preamplifier PR.

  As described above, in the amplification optical fiber 33 of the main amplifier PA, the active element is brought into the excited state by the excitation light. Therefore, when pulsed light having a reduced pulse width is incident on the wavelength selection filter FL, the excited active element causes stimulated emission by the light, and the power of the light is amplified by the stimulated emission to be amplified. Pulsed light is emitted from the optical fiber 33. Therefore, light having a narrower pulse width and amplified power than the light emitted from the seed light portion MO is emitted.

  The light emitted from the main amplifier PA propagates through the optical fiber 40 and is emitted from the fiber laser device 1.

  It should be noted that light with low power density may be emitted except when pulse light is emitted from the seed light portion MO, and the active element of the preamp PR excited by the light causes induction excitation to cause the light Is amplified. However, since the light from the seed light portion MO in this case has a small power as described above, the power of the light emitted from the preamplifier PR does not reach such a power as to be wavelength converted by the wavelength conversion portion RF. Therefore, in this case, the light emitted from the preamplifier PR is not wavelength-converted by the wavelength conversion unit RF, and the wavelength selection filter FL suppresses the incidence on the main amplifier PA.

  Next, the pulsed light emitted from the seed light portion MO will be described in more detail.

  FIG. 3 is a view showing light emitted from the seed light portion MO. The light emitted from the seed light portion MO also described in FIG. 2 is shown on the left side of FIG. 3, and the enlarged view of the portion surrounded by the broken line on the left side of FIG. There is. As shown in FIG. 3, when the pulsed light emitted from the seed light portion MO is expanded, it can be seen that small ripples are superimposed. This ripple is due to the vibration of the AOM 14 in the first state. In the first state, the AOM 14 repeats a state in which light is likely to be transmitted and a state in which light is slightly less likely to be transmitted as a result of oscillation. For this reason, there is a tendency for ripples to occur in the light transmitted through the AOM 14 and emitted according to the predetermined cycle in which the AOM 14 vibrates.

  However, as described above, in the fiber laser device 1 of the present embodiment, the respective resonance periods of the respective lights resonating in the respective light paths in the seed light portion MO and the predetermined predetermined amplitude of the AOM 14 in the first state. The cycles and the non-integer multiples are mutually related. The inventors of the present invention can suppress that the ripple is amplified when the resonance period of the resonating light and the predetermined period in which the AOM 14 vibrates in the first state are in a relation of a non-integer multiple. Found. Therefore, in the pulsed light emitted from the seed light portion MO, the amplification of the ripple generated due to the vibration of the AOM 14 is suppressed.

  Next, in the present embodiment, the relationship between the power of each light emitted from the seed light portion MO by resonating in the respective light paths of the seed light portion MO and the branching ratio in the optical coupler 16 will be described.

  FIG. 4 is a view showing the relationship between the ratio of the power of each light emitted from the seed light unit MO by resonating in each light path of the seed light unit MO and the branching ratio in the optical coupler 16. The present inventors found that changing the branching ratio changes the ratio of the power of each light resonating in each optical path, and finds that the tendency in FIG. 4 does not depend on the optical path length, wavelength, etc. The

  In FIG. 4, assuming that the length of a specific light path is the basic light path length S as described above, the distance for reciprocating the specific light path is 2S. Further, assuming that the length of the loop optical fiber 15 is a loop optical path length L, the distance traveled back and forth in the optical path that makes one round of the loop optical path in the middle of propagating a specific optical path is 2S + L. In this case, the resonating light travels the loop optical path in the forward path of the specific optical path and does not go around the loop optical path in the return path, and does not go around the loop optical path in the forward path of the specific optical path. There is a case. In addition, the distance traveled back and forth in the optical path that makes two rounds of the loop optical path while propagating on the specific optical path is 2S + 2L. In this case, the resonating light makes two rounds of the loop light path in the outward path of the specific light path and does not go around the loop light path in the return path, and does not go around the loop light path in the outward path of the specific light path. There are cases where the loop light path is made one round in the forward path of a specific light path, and the loop light path is made one round even in the return path. Similarly, while propagating on a specific optical path, the distance to reciprocate the optical path that makes three rounds of the loop optical path is 2S + 3L, and the distance to reciprocate the optical path that makes four rounds on the loop optical path becomes 2S + 4L while propagating to the specific optical path. The distance traveled back and forth in the optical path that makes five rounds of the loop optical path while propagating through the specific optical path is 2S + 5L. Also in these cases, all combinations apply as to how to go around the loop light path in the forward path and return path of a specific light path.

  As apparent from FIG. 4, when the branching ratio in the optical coupler 16 is 3 dB or less, the ratio of the power of light resonating in a specific light path without traveling around the loop light path among the respective lights resonating in the respective light paths is highest. Therefore, if the branching ratio in the optical coupler 16 is 3 dB or less, the resonance period of light resonating in a specific optical path without going around the loop optical path and the predetermined period in which the AOM 14 vibrates in the first state are noninteger multiples Relationship. In this case, it is preferable that the resonance period of the light resonating in another optical path and the predetermined period in which the AOM 14 vibrates in the first state be a noninteger multiple relationship with each other. In order to be most affected by light resonating in a specific light path, the resonance cycle of light resonating in another light path and the predetermined cycle in which the AOM 14 vibrates need not be in a relation of a non-integer multiple.

  Further, when the branching ratio at the optical coupler 16 is 3 dB or more and 4.8 dB or less, the ratio of the powers of the light resonating in the optical path that makes one round of the loop light path among the respective lights resonating in the respective light paths is highest. Therefore, when the branching ratio at the optical coupler 16 is 3 dB or more and 4.8 dB or less, the resonance period of light resonating one round of the loop optical path in the middle of the specific optical path and the predetermined period when the AOM 14 vibrates in the first state Are mutually non-integer multiples. In this case, it is preferable that the resonance period of light resonating in another optical path and the predetermined period in which the AOM 14 vibrates in the first state be a noninteger multiple relationship with each other, but the ripple is in the middle of a specific optical path The resonance period of the light resonating in the other optical path and the predetermined period in which the AOM 14 vibrates need not be in the relation of a non-integer multiple, because they are most affected by the light resonating in one loop optical path. .

  Further, when the branching ratio at the optical coupler 16 is 4.8 dB or more, the ratio of the powers of the light resonating in the optical path that makes two rounds of the loop light path among the respective lights resonating in the respective light paths is the highest. Therefore, if the branching ratio at the optical coupler 16 is 4.8 dB or more, the resonance period of light resonates twice around the loop optical path in the middle of a specific optical path, and the predetermined period in which the AOM 14 vibrates in the first state They are mutually related by a non-integer multiple. In this case, it is preferable that the resonance period of light resonating in another optical path and the predetermined period in which the AOM 14 vibrates in the first state be a noninteger multiple relationship with each other, but the ripple is in the middle of a specific optical path The resonance cycle of the light resonating in the other optical path and the predetermined cycle in which the AOM 14 vibrates do not have to be a non-integral multiple relationship with each other because the light resonates in the other optical paths most affected by the resonating light in the loop optical path. .

  Next, a pulse-like wave of light which is likely to occur when the optical path length is long will be described.

  When the basic optical path length S of a specific optical path is long, the shape of the pulse-like light to be emitted may be a shape in which a wave occurs in the Gaussian distribution shape. The period of the wave is very large compared to the period of the ripple. However, in the fiber laser device of the present embodiment, not only light resonating in a specific optical path but also light resonating in a loop optical path in addition to the specific optical path exists. Therefore, even if the basic optical path length S is long and undulation occurs in the pulse shape of the light resonating a specific optical path, the light emitted from the seed light portion MO does not go around the loop optical path but a specific optical path. The light that resonates with the light that resonates around the loop light path in the middle of the specific light path is combined, so the wave is reduced. In particular, as shown in FIG. 4, if the branching ratio of the optical coupler 16 is 2 dB or more and 8 dB or less, the power of light resonating a specific light path without going around the loop light path and one round of the loop light path The power of the light resonating in the light path and the power of the light resonating in the light path which makes two rounds of the loop light path on the way of the specific light path are balanced. Therefore, even when the basic optical path length S of a specific optical path is long, if the branching ratio of the optical coupler 16 is 2 dB or more and 8 dB or less, occurrence of waviness in the emitted pulse light is more appropriately reduced. be able to. In addition, if it is an object to reduce the occurrence of such waviness, unlike the present embodiment, in the first state, the resonance period of the light having the largest power among the respective lights resonating in the respective optical paths. The predetermined period in which the AOM 14 vibrates may not be in a relation of a non-integer multiple.

  As described above, in the fiber laser device 1 of the present embodiment, the seed light unit MO has a plurality of optical paths that are partially shared and in which the light resonates, and at least the respective light resonates in the respective optical paths. The resonance period of the light having the largest power among them and the predetermined period in which the AOM 14 vibrates in the first state are in a relation of a non-integer multiple. By setting the resonance period of the light with the largest power and the predetermined period in which the AOM 14 vibrates to be a noninteger multiple relationship with each other, it is possible to suppress that the most noticeable ripple becomes large, and the light is emitted from the seed light portion MO Light ripple can be suppressed. Therefore, the ripple of the light emitted from the fiber laser device 1 can be suppressed.

  Furthermore, in the fiber laser device 1 of the present embodiment, the respective resonance periods of the respective lights resonating in the respective optical paths and the predetermined period in which the AOM 14 vibrates in the first state are mutually in a noninteger multiple relationship. For example, the increase in ripple of each light can be further suppressed, which is preferable.

Second Embodiment
Next, a second embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component the same as that of 1st Embodiment, or equivalent, the description which attaches | subjects the same referential mark except the case where it demonstrates especially, is abbreviate | omitted.

  FIG. 5 is a view showing a fiber laser device of the present embodiment. As shown in FIG. 5, the fiber laser device 2 of the present embodiment differs from the fiber laser device 1 of the first embodiment in that the seed light portion MO is a fiber ring type fiber laser device.

  The seed light unit MO according to the present embodiment includes the excitation light source 11, the first optical fiber 18, the optical coupler 51, the amplification optical fiber 13, the optical filter 53, the second optical fiber 54, the AOM 14, and The three optical fibers 55, the optical coupler 16, the loop optical fiber 15, and the optical coupler 52 are provided as main components.

  The optical coupler 51 optically couples the core of the first optical fiber 18 and the core of the amplification optical fiber 13. Therefore, the excitation light emitted from the excitation light source 11 and propagating through the first optical fiber 18 is incident on the amplification optical fiber 13. The first optical fiber 18 of the present embodiment is different from the first optical fiber 18 of the first embodiment in that the FBG is not formed.

  The optical filter 53 is a band pass filter that transmits light of a predetermined wavelength and suppresses transmission of light of another wavelength. The optical filter 53 has, for example, the same configuration as the wavelength selection filter FL. For example, when the active element added to the amplification optical fiber 13 is ytterbium, light having a wavelength of 1060 nm is transmitted. The optical filter 53 is connected to one end of the second optical fiber 54. The second optical fiber 54 has the same configuration as the second optical fiber 19 of the first embodiment.

  The other end of the second optical fiber 54 is connected to the AOM 14. The AOM 14 of the present embodiment differs from the AOM 14 of the first embodiment in that the end face from which light is emitted is subjected to anti-reflection processing. The AOM 14 of the present embodiment transmits light incident from the second optical fiber 54 in the first state where it vibrates at a predetermined cycle. One end of a third optical fiber 55 is connected to the side opposite to the second optical fiber 54 side of the AOM 14. The third optical fiber 55 has the same configuration as the second optical fiber 54. In the first state, the AOM 14 emits the light incident from the second optical fiber 54 to the third optical fiber 55. Further, in the second state, the AOM 14 emits light incident from the second optical fiber 54 in a direction different from that of the third optical fiber 55.

  Further, an optical coupler 16 is provided in the middle of the third optical fiber 55, and in the same manner as the second optical fiber 19 and the loop optical fiber 15 are connected in the optical coupler 16 in the first embodiment. In the optical coupler 16, the third optical fiber 55 and the loop optical fiber 15 are connected.

  Further, an optical coupler 52 is provided in the middle of the third optical fiber 55 on the opposite side to the AOM 14 side with respect to the optical coupler 16. The optical coupler 52 connects the third optical fiber 55 and the optical fiber 29 of the preamplifier PR. Accordingly, the light propagating through the third optical fiber 55 branches into the optical fiber 29 at a branching ratio and propagates through the optical fiber 29.

  Further, the other end of the third optical fiber 55 is connected to the optical coupler 51. That is, the optical coupler 51 connects the end of the first optical fiber 18 and the end of the third optical fiber 55 to the end of the amplification optical fiber 13, and the core of the first optical fiber 18 and the third light The core of the fiber 55 and the core of the amplification optical fiber 13 are optically coupled.

  In the seed light portion MO of the present embodiment, assuming that the optical path including the amplification optical fiber 13, the optical filter 53, the second optical fiber 54, the AOM 14 and the third optical fiber 55 is a specific optical path, the specific optical path Is a circular optical path. Further, also in the seed light portion MO of the present embodiment, since the loop light path formed of the loop optical fiber 15 is connected to a specific light path, the seed light portion MO has a plurality of light paths. Also in this embodiment, the optical path consisting of the specific optical path and the loop optical path is an optical path different from the specific optical path, and shares a part with the specific optical path. The light propagating through this optical path is branched from the third optical fiber 55 to the loop optical fiber 15 in the optical coupler 16 and goes around the loop optical fiber 15 one or more turns, and then the optical coupler 16 It is coupled to the optical fiber 55. Further, even in the case of an optical path including a loop optical path, the optical paths are different from each other if the number of times of looping around the loop optical fiber 15 is different. Thus, since the loop optical fiber 15 is connected to a specific optical path, the optical path lengths of the respective optical paths are different from each other. Therefore, the resonance period of light resonating around a specific optical path without branching the loop optical path, and the resonance cycles of light resonating one or more rounds of the loop optical path on the way of a specific optical path It is different.

Also in the present embodiment, at least the resonance period of the light with the largest power among the lights resonating in the respective optical paths described above and the predetermined period in which the AOM 14 vibrates in the first state are mutually non-integer multiples It is related. Furthermore, it is preferable that the respective resonance periods of the respective lights resonating in the respective optical paths described above and the predetermined period in which the AOM 14 vibrates be in a relation of a non-integer multiple. For example, as illustrated in the first embodiment, it is assumed that the frequency at which the AOM 14 vibrates is 135 MHz and the vibration period is 74 × 10 ⁻¹⁰ seconds. In this case, if the length of the specific optical path is the basic optical path length S, the speed of light is 299, 792, 458 m / s, and the refractive index of the optical fiber is 1.445, the specific optical path length S is 1 m. The resonant period of the light resonating around the optical path of the optical path is about 1.0.times.10.sup.- ⁸ seconds. In this case, the resonance period of light resonating in a specific optical path and the predetermined period in which the AOM 14 vibrates in the first state are in a relation of a non-integer multiple. Also, as described above, when the basic optical path length S is 1 m and the loop optical path length L which is the length of the loop optical fiber 15 is 0.5 m, resonance occurs in the optical path which makes one loop optical path while light is resonating. The resonance period of the light is about 1.3.times.10.sup.- ⁸ seconds, and in the optical path which makes two rounds of the loop light path while the light resonates, the resonance period of the resonating light is about 1.5.times.10.sup.- ⁸ seconds. . Therefore, in this case, the respective resonance periods of the respective lights resonating in the respective optical paths and the predetermined period in which the AOM 14 vibrates in the first state are in the relation of a non-integer multiple.

  In the seed light portion MO of the present embodiment, excitation light is constantly emitted from the excitation light source 11, and in the standby state, the AOM 14 is brought into the second state. Therefore, in the standby state, even when the light emitted from the amplification optical fiber 13 is transmitted through the optical filter 53 and propagates through the second optical fiber 54, the light entering the AOM 14 from the second optical fiber 54 is , And the light is emitted to the outside without being incident on the third optical fiber 55. Therefore, the light does not go around the specific optical path or the optical path consisting of the specific optical path and the loop optical path, and the light does not resonate. For this reason, the excited state of the active element of the amplification optical fiber 13 becomes high. Also in the present embodiment, the period in which the AOM 14 of the seed light portion MO is in the second state is a period in which the amplification optical fiber 13 does not self-oscillate.

  Next, the AOM 14 is brought into the first state at a timing slightly before the point of time when the pulsed light is emitted. Then, the light entering the AOM 14 from the second optical fiber 54 is transmitted to the third optical fiber 55. For this reason, the light travels around a specific light path or a light path consisting of the specific light path and the loop light path, and the light resonates in each of the light paths. By this resonance light, the active element of the amplification optical fiber 13 brought into the high excited state as described above causes stimulated emission, the resonance light is amplified, and the pulse light is emitted from the AOM 14. To the optical fiber 29 of the preamp PR. Then, as in the first embodiment, light is amplified by the preamplifier PR and the main amplifier PA, and the amplified pulsed light is emitted from the optical fiber 40.

  As described above, among the respective lights resonating in the respective optical paths, the resonance period of the light with the largest power and the predetermined period in which the AOM 14 vibrates in the first state are in the relation of a non-integer multiple. Therefore, also in the present embodiment, it is possible to suppress ripples of pulsed light emitted from the seed light portion MO. Therefore, the ripple of the light emitted from the fiber laser device 2 can be suppressed.

  The embodiments of the present invention have been described above by way of example, but the present invention is not limited to these.

  For example, although the example in which the AOM 14 of the seed light portion MO reflects light in the fiber laser device 1 of the above embodiment has been shown, the present invention is not limited to this. For example, the end face of the AOM 14 may be non-reflection processed and a second FBG having a lower reflectance than the FBG 12 may be provided between the AOM 14 and the preamplifier PR. In this case, when the AOM 14 is turned on and light is transmitted through the AOM 14, the light is reflected by the second FBG, and oscillation can be generated between the FBG 12 and the second FBG. In this case, a specific optical path is between the FBG 12 and the second FBG.

  In addition to the seed light unit MO, the fiber laser devices 1 and 2 are provided with a preamplifier PR, a main amplifier PA, a wavelength conversion unit RF, and a wavelength selection filter FL. However, if the power of light emitted from the seed light unit MO, which is a fiber laser device, is large, the preamplifier PR, the main amplifier PA, the wavelength conversion unit RF, and the wavelength selection filter FL may not be provided.

  EXAMPLES Hereinafter, the contents of the present invention will be more specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Comparative Example
An optical system having the same configuration as that of the seed light portion MO of the first embodiment was prepared. In this optical system, the predetermined cycle in which the AOM 14 vibrates is 135 MHz. Further, in this optical system, a basic optical path length S which is an optical path length of a specific optical path from the AOM 14 to the FBG 12 without passing through the loop optical fiber 15 and a loop optical path length L which is an optical path length of the loop optical fiber 15 The relationship is as follows.
2S + 3L = 740 cm

  That is, in the present optical system, the loop optical fiber 15 is rotated three times while reciprocating between the AOM 14 and the FBG 12, and the optical path length is 740 cm. This optical path length is equal to the distance that light travels through the optical fiber for 10 cycles at a frequency of 135 MHz. That is, the resonance period of light in this optical system and the predetermined period in which the AOM 14 vibrates are in the relationship of an integral multiple of each other.

<Example>
The same optical system as that of the comparative example was prepared except that the basic optical path length was increased by 1 cm from the optical system of the comparative example, and the optical path length was 742 cm. In this optical system, the resonance period of light and the predetermined period in which the AOM 14 vibrates are in a relation of a non-integer multiple.

  Next, the temporal change of the intensity of the light emitted from the optical system of the comparative example and the example was measured. The result is shown in FIG. 6, and the part surrounded by the dotted line in FIG. 6 is shown in FIG. As shown in FIGS. 6 and 7, in the comparative example in which the resonance period of light and the predetermined period in which the AOM 14 vibrates are in the relationship of integral multiples, ripples occur. On the other hand, in the example in which the resonance period of light and the predetermined period in which the AOM 14 vibrates are in a relation of a non-integer multiple, it is shown that the ripple is suppressed as compared with the comparative example.

  As described above, according to the present invention, it was shown that the ripple of the emitted light can be suppressed as shown in the example and the comparative example.

  As described above, according to the present invention, a fiber laser device capable of suppressing the ripple of emitted light is provided, and can be used in the field using laser light such as a processing machine or a medical device.

1, 2 · · · Fiber laser device 11, 21, 31 · · · Pumping light source 13, 23, 33 · · · Amplification optical fiber 15 · · · Loop optical fiber FL · · · · · · Wavelength selection filter MO · · · species Optical part (fiber laser device)
PA: Main amplifier PR: Preamplifier RF: Wavelength converter

Claims (9)

A plurality of optical paths in which a part is shared and the light resonates,
An amplification optical fiber that is a part of each of the optical paths and amplifies each light resonating in each of the optical paths;
A first state disposed in a shared portion of each of the optical paths, and vibrating in a predetermined cycle to emit light incident from the optical path to the optical path; and emitting light incident from the optical path to other than the optical path An acousto-optic element switched to two states;
Equipped with
The resonance period of the light with the largest power among the lights resonating in the respective optical paths and the predetermined period in which the acousto-optic element vibrates in the first state are in a relation of a non-integer multiple A fiber laser device characterized by The respective resonance periods of the respective lights resonating in the respective optical paths and the predetermined periods in which the acousto-optic element vibrates in the first state are in a relation of a non-integer multiple. The fiber laser device according to Item 1. The plurality of optical paths have a specific optical path, and an optical path consisting of the specific optical path and a circular loop optical path connected in the middle of the specific optical path,
The light propagating in the specific optical path is branched to the loop optical path at a predetermined branching ratio, and the light propagating in the loop optical path is coupled to the specific optical path at the predetermined branching ratio. The fiber laser device according to claim 1. The fiber laser device according to claim 3, wherein the specific light path is a light path in which light reciprocates between a pair of reflection parts. The predetermined branching ratio is 3 dB or less, and the resonance period of the light resonating in the specific optical path and the predetermined period in which the acousto-optic element vibrates in the first state have a relationship of noninteger multiples with each other. The fiber laser device according to claim 4, characterized in that: The predetermined branching ratio is 3 dB or more and 4.8 dB or less, and the acousto-optics in the first state and the resonance period of light resonating in the optical path that travels around the loop optical path while propagating the specific optical path 5. The fiber laser device according to claim 4, wherein the predetermined period in which the element vibrates is in a relation of a non-integer multiple to each other. The predetermined branching ratio is 4.8 dB or more, and the acousto-optic element in the first state and the resonance period of light resonating in the optical path which makes two rounds of the loop optical path while propagating the specific optical path. 5. The fiber laser device according to claim 4, wherein the oscillating predetermined cycles are in a relation of a non-integer multiple. 5. The fiber laser device according to claim 4, wherein the predetermined branching ratio is 2 dB or more and 8 dB or less. The fiber laser device according to claim 3, wherein the specific light path is a circular light path.

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